Tanks can miss on ads while in a 10man it's impossible to hit cap the groups in many guilds. What are we supposed to do? Hit cap the tanks (just for one fight and spend 100-1000g each every time we switch boss)?

This is fundamentally bad design for a simple reason: It's not skill that is lacking but a mechanic that is right.

We reached a point where we faceroll - literally faceroll - phase 1, we can even move very smoothly on 3rd, but 2nd kills us most of the time because of misses by tanks.

What are we going to do, have only rogues and tanks? And how can a 10man guild do that?

I'm guessing you're talking about hit cap in relation to interrupting the adds in phase 2? If so, then you must've missed the part in the 4.1 patch notes that states that all interrupts that don't do damage will always hit, regardless of hit rating.

I agree, at least to an extent. Depending on what kind of setup you are using you can work around it.

If you have a Holy Paladin, he/she can interrupt (given they have at least 1pt in spirit > hit talent). If you can muster two interrupters you can put the two tanks on the same pillar so both do interrupts. Chances that both miss the same interrupt are mighty slim I'd think.

But like I said, I generally agree. Interrupting is such a crucial point in many encounters now (especially on heroic mode) which really hurts 10-man.

In a heroic mode of a final or near-final boss I would accept obscure mechanics such as having to hit cap or near hit cap tanks but this is a normal mode, and in a 10man it has to split the raid into 3 groups that must not miss.

Simple solution without 4.1 is: Put a debuf on ads "The Heat from the Lava surrounding the target makes it impossible for you to miss" or a buff at that phase only "Your senses are heightened making your interrupts unable to miss".

Such a solution would avoid a Game-wide change, which I suspect right now is because of Nefarian.

The game-wide change is so that hit-cap becomes less important, and in fact, it'll be above where it's possible to get. It's a good mechanical change and will affect both PvE and PvP. It's just not good mechanics to have some classes unable to miss while others struggle to make a specialized stat so high.

However, until implemented, the game includes some serious random-fail problems. Which I think was the point of the thread.